1. Field of the Invention
The present invention relates to a vibrating device, and more particularly, to a vibrating device for moving an object by vibration, that is, a vibrating device for use in a dust removing device of an optical device, such as a camera, a facsimile machine, a scanner, a projector, a copying machine, a laser beam printer, an ink jet printer, a lens, binoculars, or an image display apparatus.
2. Description of the Related Art
In recent years, an image pickup device has been improved in resolution of an optical sensor. Along with the improvement, an image taken by the image pickup device has become more seriously affected by dust that adheres to an optical system during use.
In particular, the resolution of an image pickup element of a video camera or a still camera is remarkably improving. Accordingly, if dust adheres to an optical element disposed close to the image pickup element, a defect may be caused in the image.
For example, if dust from outside or abrasion powder generated on an internal mechanical sliding friction surface adheres to an infrared cut filter or an optical low-pass filter, the dust comes out in the taken image all the more for the small amount of blurring of the image on a surface of the image pickup element.
On the other hand, an image pickup portion of a copying machine, a facsimile machine, or a scanner reads a planar document by scanning a line sensor or by scanning the original brought proximity to the line sensor. In this case, if dust adheres to a light beam incident portion with respect to the line sensor, the dust comes out in the scanned image.
In particular, in case of a device employing a system of scanning an original, such as a reading portion of a facsimile machine, or in a case of a so-called flow reading type, in which an original from an automatic original transporting device of a copying machine is read while being transported, one particle of dust comes out as a line image continued in an original transporting direction.
As a result, there arises a problem that image quality is greatly impaired.
The image quality may be restored when the dust is wiped out by manpower. However, dust that adheres during use may only be identified after image taking An image taken or scanned before the dust is identified has the dust coming out in the image, which needs to be corrected by software. Further, in a case of a copying machine, the image with the dust is simultaneously output to a medium such as a sheet of paper, which requires considerable efforts for correction.
In view of the above-mentioned problems, there has been conventionally proposed an image reading device in which dust is moved away from an image reading portion through application of a vibration (U.S. Pat. No. 7,006,138, and U.S. Patent Application No. 2009/207493).
FIG. 8A illustrates a configuration of a conventional dust-proof element portion disclosed in U.S. Pat. No. 7,006,138.
The dust-proof element portion includes a glass plate 27 serving as an optical element. A light beam passes through an imaging light beam transmissive range 27a inside the glass plate 27, and forms an image on an image pickup element (not shown).
Further, piezoelectric bodies 271, 272, 273, and 274 are fixed to the glass plate 27.
An electric terminal 275 for grounding is provided between each piezoelectric body and the glass plate 27.
Each piezoelectric body includes, in the direction of the length, sections which are alternately changed in direction of polarity (as indicated by “+” and “−” in FIG. 8A). The piezoelectric body 271 and the piezoelectric body 273 have the same polarity arrangement in the direction of the length.
Further, the piezoelectric body 272 and the piezoelectric body 274 have the same polarity arrangement in the direction of the length. When the section length of “+” and “−” is defined as λ, the polarity arrangements of the piezoelectric body 272 and the piezoelectric body 274 are each displaced by λ/4 in the direction of the length, with respect to the polarity arrangements of the piezoelectric body 271 and the piezoelectric body 273.
The piezoelectric body 271 and the piezoelectric body 273 are each applied with a voltage in the same temporal phase in the same period by an oscillator.
On the other hand, the piezoelectric body 272 and the piezoelectric body 274 are applied with a voltage shifted in temporal phase from that of the piezoelectric body 271 and the piezoelectric body 273 by a 90 degree phase shifter, in the same period by an oscillator.
FIG. 8B illustrates a traveling wave generated on a surface of the glass plate 27, which is viewed from an h direction of FIG. 8A described above.
The traveling wave travels to the right in FIG. 8B (direction of an arrow i). When the traveling wave is generated on the surface of the glass plate 27, elliptic motion in a counterclockwise direction on a plane of paper of FIG. 8B occurs at any mass point on the surface of the glass plate 27.
Accordingly, dust adhering to the surface of the glass plate 27 moves to the left in FIG. 8B, so as to be removed from the imaging light beam transmissive region 27a. 
FIG. 9A illustrates a configuration of a vibrating device of a conventional dust removing device disclosed in U.S. Patent Application No. 2009/207493.
A vibrating device 300 is provided to an image pickup element 301 which converts a received object image into an electric signal so as to generate image data.
A space in a surface (front surface) of the image pickup element 301 is hermetically sealed by the vibrating device 300 and the image pickup element 301.
The vibrating device 300 includes an optical element 302 and a pair of piezoelectric elements 303a and 303b. The optical element 302 is in the form of a rectangular plate shape. The piezoelectric elements 303a and 303b are fixed to both end portions of the optical element 302 through bonding, and each serve as an electromechanical energy converting element.
The piezoelectric element 303a is applied with an alternating voltage A, and the piezoelectric element 303b is applied with an alternating voltage B.
FIG. 9B illustrates a displacement distribution of an out-of-plane first order bending vibration A and a displacement distribution of an out-of-plane second order bending vibration B.
The longitudinal axis represents a displacement in an out-of-plane direction of a surface of the vibrating device 300, the surface being opposite to the side on which the image pickup element 301 is disposed, in which the image pickup element 301 side is defined as a negative side. As illustrated FIG. 9B, the lateral axis corresponds in position to the vibrating device 300 in the direction of the length.
The alternating voltage A and the alternating voltage B are both alternating voltages with periodicity responsive to a resonance phenomenon which occurs with the out-of-plane first order bending vibration and the out-of-plane second order bending vibration. Further, the alternating voltage A and the alternating voltage B are different from each other in temporal phase.
Accordingly, in the vibrating device 300, a combined vibration of two vibrations, namely, the out-of-plane first order bending vibration and the out-of-plane second order bending vibration which are different in temporal phase, is excited.
FIGS. 10, 11, 12, and 13 are graphs showing, for each temporal phase, displacements of the out-of-plane first order bending vibration and the out-of-plane second order bending vibration in a case where those two vibrations have a time phase difference of 90 degrees and an amplitude ratio therebetween is 1 to 1, and a displacement of a vibrator in which those vibrations are combined.
In FIGS. 10, 11, 12, and 13, a waveform C shows a displacement of the out-of-plane first order bending vibration. A waveform D shows a displacement of the out-of-plane second order bending vibration.
A waveform E shows a displacement of the vibrating device 300 in which those two vibrations are combined.
A waveform G shows a displacement of the vibrating device 300, which precedes the waveform E by 30 degrees in temporal phase.
A waveform F shows a normalized displacement rate in a Y direction in the vibrating device 300. In a case where the dust removing device is operated, dust that has adhered to a surface of the optical element 302 is applied with a force in the direction of the normal of the surface of the optical element 302 when the optical element 302 raises up the dust out of plane (in a direction (positive direction) opposite to the side on which the image pickup element 301 of FIG. 9B is disposed), and moves in a flipping manner. In other words, in each temporal phase, when the waveform F showing the displacement rate in the Y direction takes a positive value, dust is raised up out of plane and applied with a force in the direction of the normal of the waveform E showing the displacement of the vibrating device 300 in the corresponding temporal phase. Then, the dust is once detached from the original position of adhesion to be relocated to a position (moved position) different from the original position of adhesion even if the dust adheres again to the optical element. In this manner, the dust keeps moving by repeatedly being detached and relocated in a manner as described above.
An arrow h of FIGS. 10 to 13 indicates a moving direction of dust.
Referring to FIGS. 10 to 13, in a range between a position 60 and a position 300 of the optical element 302, an amount of vibration for moving dust in a positive direction of an X direction is significantly larger than an amount of vibration for moving dust in a negative direction of the X direction in one period of the vibration.
Accordingly, dust may be moved in the positive direction of the X direction.
When an effective portion of the optical element 302 with respect to the image pickup element 301 falls within the range between the position 60 and the position 300, dust may be removed from the effective portion.
However, the above-mentioned vibrating devices have problems as follows. In the vibrating device disclosed in U.S. Pat. No. 7,006,138, the end portions of the glass plate 27 interfere with the traveling direction of the traveling wave. The traveling wave is reflected by the end portions, with the result that an incident wave and a reflected wave overlap each other, which may form a standing wave which does not travel.
The standing wave does not generate the elliptic motion, which makes it difficult to move dust in only one direction.
Alternatively, if a method of eliminating the reflected wave is employed, a resonance phenomenon may be difficult to make use of, because the phenomenon occurs only when the incident wave and the reflected wave overlap each other.
As a result, a large amplitude may not be obtained, and hence the elliptic motion is also reduced in speed. Accordingly, dust is moved at a lower speed, which impairs efficiency.
Meanwhile, in the vibrating device disclosed in U.S. Patent Application No. 2009/207493, a large response amplitude is obtained due to the resonance phenomenon. However, the vibrating device 300 has many resonant modes, and hence unnecessary vibrations, other than the two desired vibrations, may also be generated.
When the unnecessary vibrations are generated, if the unnecessary vibration increases to a certain value or more, an in-plane direction of a force of raising up an object on the surface of the optical element 302 out of plane may become opposite in some areas of the surface, or the force may have a smaller number of components in the in-plane direction. In some areas, the in-plane moving directions may become opposite to each other, leading to a situation where dust cannot be moved or the force moving dust becomes smaller than the adherent force of the dust, with the result that the efficiency of moving dust is reduced.